7610

• UCREFRP Catalog Number: 7610
• Author: Wick, E. J. and J. A. Hawkins.
• Title: Colorado Squawfish Winter Habitat Study, Yampa River, Colorado, 1986-1987
• USFW Year: 1987.
• USFW - Doc Type: Final Report Year 1.
• Copyright Material: NO

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cottonwood snag, at the far end of the backwater away from the river channel. •
The most commonl y used water dUAh was 2 feet, velocity was 0 feet/second, and
the Eytb t_ rate was gravel (Tables 6-8). These radio gta ged squawfish were very
seldom observed to leave the backwater. When they did move into the main
channel they would be in continual motion and usually return to the backwater
within an hour. It should be noted that this backwater is relatively new. The
500 year flood waters in 1984 washed out a large section of bank around rock •
jetty rip-rap that had been placed along the dirt cutbanks to prevent erosion.
A wide braided channel resulted. In 1985 high spring flows consolidated the
gravel bars and formed the backwater as it appears today.
Another distinctive winter macro-habitat type was termed an embayment
(Figure 5). This large (40x200 meter) habitat was used frequently by A9, B8, •
B9, and B11 (Table 5). Similar appearing areas are fairly common on the upper
Yampa River. Initial ice formation gives areas like that portrayed in Figure 5
a uniform appearance. However closer examination by drilling through the ice
indicated a diverse number of micr - itat typed within thes-e macro-habitats.
These micro-habitat types include low velocity eddy, run, shoreline, pool, and
small backwater areas. Depths utilized ranged from 0.6 to 5.9 feet/sec with
the highest frequency (54 hours) from 0.8 feet of water (Table 6). Velocity
ranged from 0.0 to 1.0 feet/second with 0.0 velocity predominantly used (Table
7). Gravel was the most prevalent substrate used (Table 8). The diversity
found within this habitat type may be what attracts squawfish to these areas.
Four squawfish repeatedly used the area depicted in Figure 5 and fish A8 in
the Government Bridge group used areas almost identical in characteristics at
RMI 97.7 and 98.8 (Table 3). Overall, use o,f emb? ayment habitats was 38% of
total observation time. Fish B9 was observed to remain in embayment habitat at
RMI 81.1 on all observation periods. Fishes A9, B8, and B11 used this area
often, but also used a nearby run habitat at RMI 81.3- 81.4 (Figure 6).
Radiotagged fish were observed in run habitat of total observation time.
Main channel run habitat like that depicted in Figure 6 was used by 9 of 10 •
fish, however only A8 used it predominantly throughout the winter. Like
embayment habitat, these predominantly run appearing areas contained some eddy
and pool microhabitat which added to the area's diversity. Velocities ranged
from 0.0-1.9 feet/second (Table 7), depths 0.5 to 5.9 feet (Table 6), and sand
was the predominant substrate (Table 8).
•
Frazil ice
Frazil ice was most frequently encountered in run habitat (Figure 6).
When drilling holes for habitat analysis it was noted that the auger blade
would bring up turbid ice crystals containing silt, sand, pebbles, and small
stoneflies from below the solid ice. It is likely that this component of the •
frazil ice was anchor ice that had broken free from the bottom substrate.
Anchor ice usually forms on the substrate as a result of super-cooling in
shallow open riffle areas. When this layer of ice breaks free it carrys with
it small substrate particles and benthos (Ashton 1979). Radiotagged squawfish
were tracked underneath 0.1-4.7 foot-thick frazil ice which was packed up
under solid ice. This occurred on several occassions during the coldest •
periods of the winter when the occurance of frazil ice was the greatest. Over
half of the radiotagged fish (A8, A9, B8, B10, and B11) were observed in
association with frazil ice during the winter. Rather than avoiding frazil
0